中亚热带退化林地土壤有机碳及不同粒径土壤颗粒有机碳的变化

The Variation of Soil Organic Carbon and Soil Particle-Sizes in Different Degraded Forests in the Subtropical Region

采用土壤颗粒分级方法,以湘中丘陵区地域相邻、环境条件基本一致的4种林地:檵木—南烛—满山红灌草丛(LVR)、檵木—杉木—白栎灌木林(LCQ)、马尾松—石栎—檵木针阔混交林(PLL)和石栎-红淡比-青冈常绿阔叶林(LAG)为对象,研究土壤有机碳(SOC)及不同粒径土壤颗粒有机碳含量随着林地退化的变化特征,剖析林地退化对中亚热带森林SOC库的影响机制。结果表明:随着林地退化,>2μm砂粉粒百分含量增高,而<2μm黏粒百分含量下降,土壤质地粗砂化;林地SOC含量呈负指数函数下降,LAG林地SOC库以粉粒、黏粒有机碳为分配主体,PLL、LCQ、LVR林地以粉粒、砂粒有机碳为分配主体;随着林地退化,同一土层同一粒径有机碳含量呈下降趋势,砂粒有机碳含量的分配比例明显增加,黏粒有机碳含量的分配比例明显下降,同一土层颗粒有机碳(POC)/矿物结合有机碳(MOC)值增加,SOC固持和保护作用减弱,SOC稳定性下降。群落物种组成、生物量和土壤颗粒组成随着林地退化的变化是导致林地SOC含量和稳定性下降的主要因素。

Four different forest lands were chosen in the hill region of central Hunan,China.They were：Loropetalum chinense-Vaccinium bracteatum.-Rhododendron mariesii scrub-grass-land（LVR）,L.chinense-Cunninghamia lanceolata-Quercus fabri shrubbery（LCQ）,Pinus massoniana-Lithocarpus glaber-L.chinense coniferous-broad leaved mixed forest（PLL）and L.glaber-Cleyera japonica-Cyclobalanopsis glauca evergreen broad-leaved forest（LAG）.In order to elucidate the effects of forest degradation on soil organic carbon,the soil partical-size fractionation method was adopted to study the changes of soil organic carbon（SOC）concentrations and their distributions in different particle-size fractions in the mid-subtropical zone of China.The result showed that the percentage of 〉2μm particles（sand,silt）increased,while that of 〈2μm clay particles decreased,and soil texture was coarse sand with the degradation of forest land.SOC concentration had the negative exponential function decreasing trend with the degradation of forest land.SOC pool was mainly composed of silt-C and clay-C in LAG,while those were dominated by silt-C and sand-C in PLL,LCQ and LVR.With the degradation of forest land,Concentrations of SOC in three partical-sized fractions were decline,the distribution proportion of sand-C concentrations increased obviously,but that of clay-C decreased obviously,and the ratio of POC/MOC increased,the SOC fixation,protective effect,stability decreased in the same layer.The changes of community species composition,biomass and soil particles composition with the degradation of forest land were the main factors leading to the decrease of SOC contents and stability of forestlands.